Contact for error resistant coupling of electrical signals

ABSTRACT

A signal connector assembly with a plug contact within a plug having a high resistive portion. When the plug of the assembly first makes contact with the electrical receptacles within a mating receptacle, the high resistive portion prevents a voltage surge. As the plug is further inserted into the receptacle, the energy passing from the plug to the receptacle is gradually increased. Eventually, the receptacle contacts within the receptacle pass the high resistive portion and make contact with the conductive portion of the plug contact, thereby permitting transmission of valid signals without the generation of spurious errors.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates generally to electrical connectors forelectronic devices. More particularly, the invention relates toelectrical contacts for use in electrical connectors to prevent thegeneration of spurious signals upon mating of the connector.

[0003] 2. Description of the Related Art

[0004] Electrical connectors for use with peripheral electronic devicesare well known in the art. A recurrent problem with many prior artconnectors is the generation of spurious signals upon mating of aperipheral electronic device to an electronic system which is alreadyenergized. The connector may induce a voltage pulse into the energizedelectronic system. The voltage pulse may travel through the electronicsystem, thereby introducing spurious errors into the system. Thisproblem is known in the art as the “hot plug” problem.

[0005] This condition that causes errors in electronic systems resultsfrom the very high data rates and very low energy of the signals withinthe systems. The input capacitance of the connector, printed circuitboard lines and device capacitance of the buffer integrated circuitdevices are the basis of the problem. Energy must flow from the systembus to charge this input capacitance, (generally tens of picofarads).When energy is removed from the system bus, a voltage pulse to anadjacent device on the bus occurs, thereby creating errors in thesystem. The voltage pulse may be no greater than normal signals so nonew radiated noise problem is introduced. However, it can cause data tobe incorrectly transferred. Accordingly, the interconnections themselvesare a large portion of the problem. This problem is universal since itaffects both digital and analog electronic devices.

[0006] The prior art has generally addressed the “hot plug” problem byusing logic and timing control circuitry, such as that which isdisclosed in U.S. Pat. No. 4,245,270, to slowly ramp up the voltagewithin the connecting line. However, providing the additional circuitryis complex and expensive.

[0007] Many connecting schemes require certain portions of the connectorto be mated prior to other portions, or in a particular sequence. Forexample, with respect to power applications, U.S. Pat. No. 4,079,440discloses a circuit board having two connector plugs of differinglengths. The longer connector plug makes initial contact with a powerline prior to the shorter plug, which reduces the onset of power surges.However, this scheme requires manual dexterity and specific insertionand removal timing for proper operation.

[0008] A connector assembly disclosed in U.S. Pat. No. 4,747,783attempts to eliminate timing and control circuitry for powerapplications. This connector assembly uses a long pin in the “plug” tofirst make contact with its mating “socket” to gradually increase thevoltage to the socket until the entire plug makes mating contact withthe socket. The plug comprises a pin having a thin insulating materialcovering the surface and a thin low resistive material covering theinsulating material. When the plug makes initial contact with thesocket, the current must pass through the resistive portion of the plug.This permits the electronic components in the peripheral device tocharge gradually and eliminates the current surges which may result.

[0009] This device is undesirable for several reasons. First, itrequires the use of several contacts of differing lengths, therebyraising manual dexterity problems. Secondly, although the low resistance(i.e. 2-60 ohms) is sufficient to eliminate current surges in powertransmissions, it is not sufficient to eliminate the voltage pulse frombeing introduced into the electronic system. In addition, the thin layerof low resistive material surrounding the thin layer of insulatingmaterial introduces an additional problem into the connection betweenthe peripheral device and the electronic system; short capacitance. Asexplained previously, capacitance is undesirable in a connector.

[0010] It would be desirable to provide a signal connector assembly thatwould not introduce errors into an electronic system during a hot plug.

SUMMARY OF THE INVENTION

[0011] The present invention provides a plug contact having a highresistive portion within a plug for use in a signal connector assembly.When the plug of the assembly first makes contact with the receptaclecontacts within a mating receptacle, the high resistive portion of theplug contact prevents a voltage spike. To prevent voltage pulses,resistive portions with resistances ranging from 10 KW to 1 GW arenecessary depending upon the application. As the plug is furtherinserted into the receptacle, the energy flow is gradually increased.Eventually, the receptacle contacts within the receptacle pass the highresistive portion and make contact with the conductive portion of theplug contact, thereby permitting transmission of valid signals withoutthe generation of spurious errors. In an alternative embodiment, thereceptacle contact, or both the plug contact and the receptacle contact,may have the high resistive portion.

[0012] It is an object of the present invention to provide a connectorassembly which permits connection of a peripheral device to an energizedelectronic system without introducing any spurious errors into thatsystem.

[0013] Other objects and advantages of the present invention will becomeapparent after reading the detailed description of the presentlypreferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is an isometric view of a simplified illustration of thepresent invention.

[0015]FIG. 2 is a graph of voltage versus distance traveled along thehigh resistive portion.

[0016]FIG. 3 is a graph of megaohms versus distance traveled along thehigh resistive portion with curves depicting varying thicknesses of theportion.

[0017]FIG. 4 is a graph of megaohms versus distance traveled along thehigh resistive portion with curves depicting varying resistivities ofthe portion.

[0018]FIG. 5a is an alternative embodiment of the present invention witha tapered high resistive portion.

[0019]FIG. 5b is an alternative embodiment of the instant invention witha stepwise-tapered high resistive portion.

[0020]FIG. 5c is an alternative embodiment of the present invention witha resistive portion of mixed high resistive materials.

[0021]FIG. 5d is an alternative embodiment of the present invention witha conductive barb in the high resistive portion.

[0022]FIG. 5e is an alternative embodiment of the present invention withthe high resistive portion extending into a hole in the conductiveportion.

[0023]FIG. 5f is an alternative embodiment of the present invention witha high resistive housing.

[0024]FIG. 5g is an alternative embodiment of the present invention witha high resistive inset in the housing.

[0025]FIGS. 5h and 5 i are an alternative embodiment of the presentinvention with a high resistance inset in the housing.

[0026]FIG. 6 is an illustration of the instant invention utilized on acircuit board.

[0027]FIG. 7 is an illustration of the instant invention being used on acylindrical connector.

[0028]FIG. 8 is an illustration of the various prior art connectors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0029] The preferred embodiment will be described with reference to thedrawing figures wherein like numerals represent like elementsthroughout.

[0030] Referring to FIG. 1, the preferred embodiment of the connectorassembly of the present invention comprises a plug 6 for mating with acorresponding receptacle 8. It should be recognized that although onlyone plug contact 7 is shown in detail for simplicity, there aretypically at least two or more plug contacts 7 within every plug 6 formating with corresponding receptacle contacts 15. The shape of the plug6 is not central to the present invention. For simplicity, the plug 6and plug contact 7 are illustrated as rectangular, although those ofskill in the art will realize that many other shapes could be usedwithout departing from the spirit of the present invention. The plugcontact 7 comprises a conductive portion 14 which can be made from anyconductive material, (such as brass, nickel, gold, copper or asuperconductor, etc.) and a highly resistive portion 12. The resistiveportion 12 is generally rectangular shaped and extends across the widthW of the plug contact 7. The resistive portion 12 comprises a layer ofhighly resistive material inset into the surface 16 of the plug 6, witha first end 11 of the resistive portion 12 exposed to the receptacle 8and a second end 13 of the resistive portion 12 in contact with theconductive portion 14.

[0031] A typical receptacle 8 includes a receptacle contact 15 for eachcorresponding plug contact 7 which electrically mates with itscorresponding receptacle contact 15 as the plug 6 of the peripheraldevice (not shown) is inserted into receptacle 8 of the electronicsystem (not shown).

[0032] In operation, the first end of the plug 6 is inserted into thecavity of the receptacle 8. The receptacle contact 15 will make firstcontact with the resistive portion 12. Since it is contemplated that theelectronic system will be energized, this will permit energy from theelectronic system to begin flowing from the receptacle contact 15,through the resistive portion 12 and into the conductive portion 14 ofthe plug contact 7. The resistive portion 12 reduces the magnitudevoltage pulses such that they will not present errors into theelectronic system, as will be explained in detail hereinafter. A portionof the voltage “seen” by the plug 6 will drop across the resistiveportion 12. As the plug 6 is inserted further into the receptacle 8, thereceptacle contact 15 passes along the surface 16 of the resistiveportion 12 until it finally reaches the conductive portion 14 of theplug contact 7. When the plug 6 is fully inserted into the receptacle 8,the receptacle contact 15 will be in direct contact with the conductiveportion 14 of the plug contact 7. Accordingly, there will be no voltagedrop across the resistive portion 12 of the plug contact 7. With respectto capacitance, the arrangement of the present invention specificallylimits the capacitance between the metallic portions of the plug andreceptacle contacts 7, 15, (it bypasses the high resistance), to anacceptably low level. It does this by minimizing their effectivecoupling area and the effective dielectric constant between them, whichis primarily air.

[0033] A primary aspect of preventing a voltage pulse is to reduce theinitial voltage seen by plug contact 7 upon insertion of the plug 6 intothe receptacle 8. Referring to the test setup 94 and the graph of FIG.2, it can clearly be seen that the resistive portion 12 reduces theinitial voltage seen by the receptacle contact 15. The graph representsthe voltage seen by the receptacle contact 15 as the plug 6 is removedfrom the receptacle 8. Referring to the portion of the graph to the leftof point 92, this shows a short circuit voltage of 0V across the plugcontact 7 while the plug contact 7 is in full contact with thereceptacle contact 15. At point 92, the receptacle contact 15 contactsthe resistive portion 12. The resistive portion 12 permits the voltageas seen across the receptacle contact 15, to increase gradually alongthe sloped (or curved) portion 93 of the graph as the plug 6 is removedfrom the receptacle 8. At point 91, the receptacle contact 15 no longercontacts the plug contact 7. Accordingly, 5V is seen by the receptaclecontact 15. Curve 93 shows the gradual transition between points 91 and92 which prevents voltage pulses which will prevent the introduction oferrors into the system. Obviously, one skilled in the art would clearlyrecognize that the graph would be reversed upon insertion of a plug 6into a receptacle 8.

[0034] The high resistance of resistive portion 12 limits the rate offlow of current from the system bus to the “cold” device beinghot-plugged into the system. The evidence of too fast a current transferis a transient voltage pulse at the connection to the operating system.The transient voltage pulse decays as it propagates along the systembus, primarily because the bus and other attached devices are sources ofcharge. Accordingly, the high resistance slows the charge transferenough to provide time for the charge to be adequately replaced. If thevoltage cannot dip below the sensing threshold of an adjacent device, anerror cannot occur.

[0035]FIG. 3 is a graph of the electrical resistance as measured fromthe end of the plug contact 7. This graph is based on a resistiveportion 12 of a rectangular shape 13 mils wide and 15 mils long. Thehigh resistive material had a resistivity of 9×10¹⁰ ohm-inches. Asshown, the resistance increases as the thickness of the resistiveportion 12 increases. Referring to curve 20, when a resistive portionthickness of 8 mils is used, a resistance of 10 MW is achieved at thefirst end 11 of the plug contact 7, which gradually decreases until thesecond end 13 is reached where the resistance is nominally zero. Curves21, 22 and 23 illustrate that the resistance decreases with a decreasein resistive portion thickness. The shape of the curves also differs asthe resistive portion thickness is changed.

[0036] Referring to FIG. 4, the thickness of the resistive portion 12was kept constant at 4 mils while the resistivity of the resistiveportion 12 was varied. Curve 31 illustrates a high resistivity of1.8×10¹¹ ohm inches. The resistance measured at the first end 11 of theplug contact 7 is almost 16 megohms, which decreases gradually to zeroat the second end 13. Curves 32 and 33 illustrate that as theresistivity of the material is decreased, the resistance measured alongthe plug contact 7 will also decrease.

[0037] By changing both the resistivity and the thickness of theresistive portion 12, as those skilled in the art will realize, thepresent invention can be adapted to different uses and applications.However, it is also extremely important to reduce the short capacitanceto a negligible level. The short capacitance is reduced by keeping thethickness of the inlay 12 relatively thick, (i.e. in applying thepresent invention to a SCSI Bus, typically approximately 5 mils). Byadjusting the resistivity and thickness of the portion, connectorassemblies can be created with desirable characteristics by preventingvoltage surges for various types of signals and applications.

[0038] Alternative embodiments of the present invention are shown inFIGS. 5a-5 h. In the embodiment depicted in FIG. 5a, the resistiveportion 12 has a tapered profile. By varying the shape of the taperedprofile 13, the resistive transition curves that result as thereceptacle contact 15 passes over the resistive portion 12 can be variedas desired for a particular application.

[0039]FIG. 5b depicts an alternative embodiment with the resistiveportion 12 in a stepwise-tapered profile 17. By varying the stepsbetween the steps, the resistive transition curves can be varied asdesired.

[0040] A third alternative embodiment is shown in FIG. 5c. The resistiveportion 12 consists of two or more materials with varying resistivities.

[0041]FIG. 5d, a fourth alternative embodiment shows, the resistiveportion 12 extending from the conducting portion 14. A conducting barb18 extends from the conducting body 14 into the resistive portion 12. Afifth alternative embodiment, FIG. 5e, has the resistive portion 12extending into a hole 19 in the conducting portion 14. As those skilledin the art will note many other variations are possible withoutdeparting from the spirit of the invention. These varying embodimentscan be used for varying the resistive transition curves for differingapplications.

[0042]FIG. 5f depicts a sixth embodiment. The conductive body 14 issurrounded by a high resistive housing 30. Receptacle contact 15 firstmakes contact with high resistive housing 30. As the receptacle contact15 makes contact with conducting portion 14, the receptacle contact seesessentially no resistance.

[0043] In FIG. 5g, the housing 30 is non-conductive. However, highresistive portions 12 make initial contact with receptacle contact 15.The high resistive portions 12 are electrically connected and may bephysically connected (not shown) to conducting portion 14.

[0044]FIGS. 5h and 5 i depict a plug 7 having a housing 85 surrounding afirst high resistance 31 portion and a second low resistance portion 32.Upon full mating, the receptacle contact 15 is in full contact with thelow resistance portion 32.

[0045]FIG. 6 illustrates that the present instant invention may also beused with the contacts on a printed circuit board. The resistiveportions 70A-N of the instant invention may be employed in one or moreplug contacts 72A-N on a conventional printed circuit board 71. FIG. 7shows that the present invention may be adapted to various shapedapplications. For instance, a plug 83 with a cylindrical shape with aresistive portion 81 and conductive portion 82. Receptacle contacts 84within the receptacle 85 make contact with the resistive portion 81prior to the conductive portion 82.

[0046]FIG. 8 illustrates some prior art electrical connectors. The sizeand shape of the connectors vary. As those skilled in the art willrealize, the present invention can be used with the contacts withinthese various connectors.

[0047] Although the invention has been described in part by makingdetailed reference to certain specific embodiments, such details areintended to be instructive rather than restrictive. It will beappreciated by those skilled in the art that many variations may be madein the structure and mode of operation without departing from the spiritand scope of the invention as disclosed in the teachings herein.

What is claimed is:
 1. An improved contact for error resistant couplingof electrical signals comprising: a contact mating portion havingselectively configured surface portions for slidingly engaging a matingcontact to continuously define an electric signal connection between thecontact and the mating contact which being mated together includes: aleading surface portion for initial engagement with the mating contactto produce an initial high resistance connection, and a trailing surfaceportion for engagement with the mating contact when in a fully matedrelationship to produce a relatively low resistance connection; saidleading surface portion being defined by a material having a resistanceof at least 10 KW; and said trailing surface portion being defined by aconductive material.
 2. The improved contact as described in claim 1wherein said leading surface portion is contiguous with said trailingsurface portion to define a continuous surface.
 3. The improved contactas described in claim 1 further comprising an intermediate surfaceportion defined by a material of lower resistivity than said leadingsurface material; wherein said mating contact sequentially engages saidleading portion, said intermediate portion, and said trailing portion.4. The improved contact as described in claim 3 wherein saidintermediate surface portion is contiguous with said leading surfaceportion and said trailing surface portion to define a continuoussurface.
 5. The improved contact as described in claim 1 wherein saidleading surface portion has decreasing thickness along the direction ofsliding engagement.
 6. The improved contact as described in claim 1wherein said leading surface portion has decreasing resistivity alongthe direction of sliding engagement.
 7. The improved contact asdescribed in claim 2 wherein the leading portion material is inset inthe trailing portion material.
 8. The improved contact as described inclaim 7 wherein said trailing portion material has a protrusionextending into said leading portion material.
 9. The improved contact asdescribed in claim 7 wherein said leading portion material has aprotrusion extending into said trailing portion material.
 10. Theimproved contact as described in claim 1 wherein said leading surfaceportion being defined by a material having a resistance between 10 KWand 1 GW.
 11. An improved connector assembly for error resistivecoupling of electrical signals comprising: a first contact and a matingcontact; said first contact comprising: a contact mating portion havingselectively configured surface portions for slidingly engaging saidmating contact to continuously define an electric signal connectionbetween said first contact and said mating contact which being matedtogether includes: a leading surface portion for initial engagement withthe mating contact to produce an initial high resistance connection, anda trailing surface portion for engagement with the mating contact whenin a fully mated relationship to produce a relatively low resistanceconnection; said leading surface portion being defined by a materialhaving a resistance of at least 10 KW; and said trailing surface portionbeing defined by a conductive material.
 12. The improved connectorassembly as described in claim 11 wherein said leading surface portionis contiguous with said trailing surface portion to define a continuoussurface.
 13. The improved connector assembly as described in claim 11further comprising an intermediate surface portion defined by a materialof lower resistance than said leading surface material; wherein saidmating contact sequentially engages said leading portion, saidintermediate portion, and said trailing portion.
 14. The improvedconnector assembly as described in claim 13 wherein said intermediatesurface portion is contiguous with said leading surface portion and saidtrailing surface portion to define a continuous surface.
 15. Theimproved connector assembly as described in claim 11 wherein saidleading surface portion has decreasing thickness along the direction ofsliding engagement.
 16. The improved connector assembly as described inclaim 11 wherein said leading surface portion has decreasing resistivityalong the direction of sliding engagement.
 17. The improved connectorassembly as described in claim 12 wherein the leading portion materialis inset in the trailing portion material.
 18. The improved connectorassembly as described in claim 17 wherein said trailing portion materialhas a protrusion extending into said leading portion material.
 19. Theimproved connector assembly as described in claim 17 wherein saidleading portion material has a protrusion extending into said trailingportion material.
 20. The improved connector assembly as described inclaim 11 wherein said leading surface portion being defined by amaterial having a resistance between 10 KW and 1 GW.
 21. The improvedconnector assembly as described in claim 11 wherein said first contacthas a housing; said leading surface portion is part of the housing andis electrically connected to said trailing portion.
 22. The improvedconnector assembly as described in claim 11 wherein said first contacthas a high resistive housing which makes contact with said trailingportion material; said leading surface portion is part of the housing.23. The improved connector assembly as described in claim 11 whereinsaid first contact is made of an anisotropic resistive material with ahigh resistive portion and a low resistive portion; said first contactsurface portion being a part of said high resistive portion; and saidsecond contact surface portion being a part of said low resistiveportion.
 24. An improved contact as described in claim 11 wherein saidfirst contact has a housing; said leading surface portion is part of thehousing and is electrically connected to said trailing portion.
 25. Animproved contact as described in claim 11 wherein said first contact hasa high resistive housing which makes contact with said trailing portionmaterial; said leading surface portion is part of the housing.
 26. Animproved contact as described in claim 11 wherein said first contact ismade of an anisotropic resistive material with a high resistive portionand a low resistive portion; said first contact surface portion being apart of said high resistive portion; and said second contact surfaceportion being a part of said low resistive portion.